More drought, floods predicted for the Amazon

It’s been estimated that the 2005 drought in the Amazon resulted in as much CO2 emissions as the entire United States emits in a year.

New research finds that climate models project big increases in the frequency and area of drought in the Amazon.

Climate models also predict that the rainy season will get wetter, the dry season will get drier and increased extreme precipitation are in store for the Amazon.

Sao Paulo, Brazil’s most populous city, is currently suffering from a severe drought. Meanwhile, over the past year, record floods have hit other parts of Brazil.

Though Sao Paulo is hundreds of miles from the rainforest, a study released earlier this year by one of Brazil’s top climate scientists found that deforestation in the Amazon is at least partially to blame for the drought gripping the city and much of the southeastern part of the country.

These types of “hydrological extremes” are becoming more frequent in Amazonia. A drought in 2005 was considered a once-in-100-years event until it happened again — this time worse — in 2010.

In addition to deforestation, government officials also blame global warming for the extreme weather. “Climate change has arrived to stay,” said Geraldo Alckmin, the governor of São Paulo State, according to the New York Times. “When it rains, it rains too much, and when there’s drought, it’s way too dry.”

New research has concluded that the Amazon will see even more of these hydrological extremes in the future, with most of the region experiencing much more frequent and extensive drought. The results were summarized in a paper recently published in the Proceedings of the National Academy of Sciences.

Dry season soy field in the Southeastern corner of the Amazon. Photo by Chris Linder.

The fact that the 2005 and 2010 droughts happened so close together made researchers at the Carnegie Institution for Science at Stanford University wonder if climate change was increasing their likelihood.

Lead author Philip Duffy, who was a visiting scholar at the Carnegie Institution for Science when the study was performed and is now the executive director of the Woods Hole Research Center, said there are a number of reasons why it’s critical for us to better understand how climatic changes are affecting precipitation patterns in the Amazon.

“Perhaps the most important of these is that droughts in the Amazon can result in very large emissions of CO2 to the atmosphere, which worsen climate change,” Duffy told Mongabay. He points out that it’s been estimated that the 2005 drought resulted in as much CO2 emissions as the entire United States emits in a year — and the 2010 drought resulted in even higher amounts of CO2 being released into the atmosphere.

The emissions caused by droughts take place over an extended period as dead trees decay, Duffy says. “But once the drought occurs the emissions are inevitable.”

Duffy and team consulted 35 climate models used by the UN’s Intergovernmental Panel on Climate Change and found they accurately represented the mechanisms that have led to previous droughts.

The models also predicted that the area of the Amazon affected by mild and severe drought will double in the eastern part of Amazonia and triple in the west by 2100. Meanwhile, a wetter wet season and more rainfall could lead to more floods, as well.

“In most of the Amazon, we find that climate models project great increases in the frequency and area of drought,” Duffy said. “The models also project that the rainy season will get wetter, and the dry season drier. They also project increases in extreme precipitation. So, all in all, climate models project an intensification of hydrological extremes in the region.”

The study did not, however, account for the effects of global warming, which tend to make drought more intense by drying out the soil. “That is to say, in our study we measured drought in terms of precipitation deficits,” Duffy explained. “Warming on top of this — which is virtually certain to occur — will make droughts more severe.”

Duffy’s co-author, Paulo Brando, who has also left the Carnegie Institution for Science for the Woods Hole Research Center, said that while we know extreme periods of wetness and dryness will impact the Amazon, we still don’t know how big of an impact they will have.

“We know that these results are important for forest dynamics, forest fires, food production; river transportation, hydroelectric power and flooding. However, we are still figuring how important they are,” Brando said in a statement.

Dr. Paulo Moutinho of the Amazon Environmental Research Institute, who was not involved in the study, said in a statement that all Amazonian countries should pay heed to the study’s results and work to rehabilitate forests while stopping deforestation.

“Beyond the implications for the Amazon forest related to climate change, this important study represents a clear alert to Brazil and other Amazonian countries that only forest conservation on a large scale will reduce a risk of a forest and regional agriculture collapse in the future.”